Kiln No. 2 at the Cemex cement plant off Cobb Road rotates slowly and steadily. Cylindrical in shape and suspended about three stories off the ground, the kiln is big enough to drive a Volkswagen through, and it throws off intense heat that quickly draws beads of sweat from the foreheads of hard-hatted visitors.

Nearby, just in front of a cliff of mined land, sit piles of the kiln's jet-black primary fuel source: Appalachian coal.

The coal also fuels an on-site power plant, owned and operated by Central Power & Lime, that sells electricity back to the grid.

The cement plant, quarry and power plant have stoked Hernando's economic engine for years, providing hundreds of jobs and injecting hundreds of millions of dollars into the local economy through employee wages and property taxes.

There is, of course, an environmental price for this productivity.

Burning coal and processing limestone to make cement emits mercury, which mixes with rain and becomes methylmercury, a neurotoxin that can impair the brain development of fetuses and young children. Other pollutants include sulfur dioxide, which causes coughing and wheezing, and carbon dioxide, the main cause of global warming.

Now both companies are embarking on efforts to reduce the amount of air pollution that spews from their stacks.

Cemex is currently testing biofuels such as peanut hulls and wood chips.

Central Power & Lime has applied for a permit to convert its plant to a biomass system, eliminating the need for coal.

Though minimizing the facilities' environmental impact is important, new energy sources are also vital to the company's long-term health, Cemex officials say.

"We want to reduce our carbon footprint," said Jim Daniel, manager of the Brooksville South plant, "but the larger issue is fuel cost."

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One of the most striking aspects to visitors of the Cemex plant is the sheer scale of the massive steel-gray infrastructure of pipes, stacks and towers.

Among the tallest structures is the preheating tower, where raw materials — aluminum, iron and limestone rock mined from the quarry — tumble into a combustion chamber called a precalciner.

The materials then drop into the kiln, where they are heated to about 2,800 degrees Fahrenheit and fuse into pebble-sized pieces called clinker. The clinker is cooled and ground into a fine powder called Portland cement.

During a tour last week, Cemex production manager Steve Bassler walked up to the large bin at the base of the preheating tower. The material in the bin looked like dirty dryer lint and smelled like rubber.

The so-called tire fluff is the polyester cord harvested from old tires when the steel belts and rubber are removed.

The company is also testing two biomass fuels: peanut hulls and wood chips.

All three materials work relatively well, but they pose some challenges, Bassler said.

A handful of coal packs a lot more energy than a handful of peanut hulls, and it's difficult to get enough of the material to provide a comparable amount of energy. Another challenge is inconsistent quality.

"All of this stuff is somebody else's waste," Bassler said.

The new alternative fuels account for only about 10 percent of the fuel used for Kiln No. 2. Still, the materials have potential to offset a significant amount of coal consumption. Cemex's plant in Clinchfield, Ga., derives 30 percent of its energy from biomass fuels.

Coal and the new alternative fuels are not the only sources of alternative energy at the plant.

Cemex and other cement producers have for decades burned whole tires in their kilns. According to the federal Environmental Protection Agency, tires deliver 25 percent more energy than coal, with an emission profile of greenhouse gases and other pollutants that is about the same, making them acceptable as an industrial fuel. Environmentalists criticize this practice, however.

Cemex has four kilns in Hernando County: two at the Brooksville South plant and two at the Brooksville North plant off U.S. 98. Two of the four have been shut down, and another is idle.

The newest of the four, Kiln No. 2 is operating at about two-thirds capacity because of a sharp dropoff in market demand. Planning for the economy's eventual recovery, the company has secured a permit from the state Department of Environmental Protection to increase the kiln's capacity from 2,800 tons per day to 3,500.

Last year, biomass fuels accounted for about 7.5 percent of Cemex's fuel use nationwide. The company is on track to increase that figure to a little more than 10 percent this year, said spokeswoman Sara Engdahl.

It's good environmental stewardship and good business, Engdahl said. Every percentage point of primary fuel substitution saves Cemex approximately $650,000 across its U.S. operations.

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Burning coal, however, accounts for only a portion of a cement kiln's total mercury emissions. The chemical reaction caused by heating the raw materials also produces mercury.

In 2008, EPA reports indicated that the Brooksville Cemex operation emitted 134 pounds of mercury, placing it among the top 20 cement kiln mercury polluters in the nation. That was the year Kiln No. 2 was put into operation.

Last year, the DEP fined Cemex $525,000 after mercury emissions measured nearly 10 times acceptable levels on 72 days. The company worked with the department on a plan to bring the kiln back into compliance.

The EPA has created new rules that would require more than 90 percent reductions in mercury and other harmful emissions. The agency estimates it would cost the industry nearly $1 billion to clean up the air pollution, but says the new standards could save up to 2,500 lives and avert thousands of asthma attacks when implemented in 2013.

Cement industry officials put the financial cost at three times that figure and say the rules would drive production overseas, doing more damage to a domestic industry already hobbled by the recession.

This month, at the urging of cement industry lobbyists, the House passed HR 2681, the Cement Sector Regulatory Relief Act, which would roll back the cement rules. The bill faces little chance in the Democratic-controlled Senate, though.

"The legislation we support is not designed to eliminate regulations, but instead provides the opportunity to continue dialogue with EPA that hopefully will result in regulations that are fair, balanced and achievable," Engdahl said.

Rep. Rich Nugent, R-Brooksville, was among those who voted yes.

"Listen, my kids breathe the same air that yours do," Nugent said in a statement last week. "Nobody is telling the EPA they can't regulate cement manufacturing, but by their own admission, there isn't a cement facility in the country that can comply with this new proposal. At least 12 facilities will close because of it, the manufacturing will move offshore, the prices will go up and we've got thousands of jobs riding on it.

"All Congress is asking for is that the EPA consider the toll on families if they go through with this," Nugent said. "People are hanging on to their jobs for dear life, and that makes it a tough and necessary balancing act."

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Just steps away from Kiln No. 2 is the Central Power & Lime plant.

Built in 1984, years before Cemex bought the cement and quarry operations, the 125-megawatt plant does not provide power directly to the Cemex operation. Rather, it sells electricity for use by utility companies.

It is the power plant that purchases — and uses most of — the coal delivered to the site.

This past summer, the NAACP released a report that ranked 431 coal-burning power plants in the country. The report, Coal Blooded: Putting Profits Before People in Florida, scored plants on five factors: sulfur dioxide and nitrous oxide emissions, the total population living within 3 miles, and the median income and percentage of "people of color" among the total population living within 3 miles.

The Central Power & Lime plant scored a D+.

Under a proposed conversion plan submitted to the DEP, the plant would produce 70 to 80 megawatts and be fueled completely by biomass, such as agricultural crops and byproducts, landscape and yard trimmings, and logging and lumber mill residues.

Central Power & Lime is owned by Arroyo Energy, a subsidiary of J.P. Morgan and Co. A spokeswoman said the company would not comment on the NAACP report or its plan to convert the plant, and declined a request from the St. Petersburg Times to tour the facility.

According to the DEP permit application currently under review, the conversion would reduce overall emissions of regulated air pollutants by "several thousand tons per year, and offer the opportunity to supply renewable power to Florida utilities."

The DEP is reviewing the permit and must respond by Oct. 26. It's unclear how soon construction would begin after a permit is issued.

Moving away from burning coal in favor of biomass is a positive development, but it's a baby step compared to the necessary paradigm shift toward renewable energy sources such as wind and solar power, said Aliki Moncrief, state director for Environment Florida, an environmental advocacy group.

"The answer needs to be renewables, and it would be wonderful if companies like Cemex could throw their buying power behind things like solar," Moncrief said. "If they move in that direction, they could have a pretty big influence on the market."

Tony Marrero can be reached at (352) 848-1431 or tmarrero@sptimes.com.